It is well known to those skilled in the art of textile finishing that wrinkle-resistance and smooth drying properties are imparted to cellulosic or cellulsoic blend textiles by chemical treatment which form covalent crosslinks between cellulose molecules in the fibers of these textiles. The crosslinks hold the cellulose molecules in place and therefore impart resilience and a preferred configuration to the cellulosic fibers. As a result, the finished textile has resistance to wrinkling during use and laundering and also permanent creases or flat seams which cannot be removed without employing chemical reactions which removes the crosslinks between the cellulose molecules.
In the textile finishing industry, the conventional method of forming crosslinks in cellulosic textiles involves the use of a pad-dry-cure process in which a methylol crosslinking reagent, such as dimethyloldihydroxyethyleneurea, methylol melamines, or formaldehyde is reacted with the cellulose of the fibers in the presence of an acidic catalyst, usually a latent acid metal salt such as magnesium chloride or zinc nitrate. More recently, the state of the art has been improved by the discovery that polycarboxylic acids, when used as catalyst in methylol crosslinking reactions with cellulose, become attached to the cellulose fibers and are thus permanently available to catalyze recuring reactions. In such recuring processes, which may be performed at any time after the original cure, the methylol crosslinks are moved within the cellulose matrix and a new preferred configuration is imparted to the cellulosic fiber. As a result, such recurable fabrics may be heat formed into new, permanent configurations, such as new sharp creases, flat seams, or hems without adding chemical reagents and while still retaining desirable durable press properties. That invention has been disclosed as U.S. Pat. No. 3,776,692, issued on December 12. 1973. The polycarboxylic acids of the above invention are organic compounds containing three or more carboxyl groups per molecule. They are specialty organic compounds which are not produced in large amounts and therefore are very costly for use in large-scale textile finishing processes. In addition, those acids are used as the free carboxylic acids, not as partial salts of the acids.
It has also previously been disclosed that amic acids react with cellulosic fibers. This reaction results in the attachment of the amic acid molecules to the cellulose molecules by way of ester groups. Ammonia is lost during the reaction with the result that free carboxylic acid groups become attached to the cellulose fiber. The reactions of amic acids with cellulose are more fully disclosed in U.S. Pat. No. 3,555,585 and No. 3,671,184, to Cuculo. In these patents, large concentrations of amic acids or anhydride/ammonia solutions are applied to rayon textiles to produce modified textiles which are not crosslinked but have high water absorption. These patents do not disclose or speculate on the use of amic acid as catalysts for methylol crosslinking reactions, either simultaneously with or subsequent to their application to the cellulosic textile, and much less as catalysts for subsequent recuring reactions of methylol crosslinks.
The reaction of polycarboxylic acids with fibrous cellulose has been disclosed by Rowland, et al. in U.S. Pat. No. 3,526,048. This patent also discloses the use of carboxylic acids which are partially neutralized by alkali metal bases, ammonia, or organic amines. The polycarboxylic acids are used as the only crosslinking reagents in this process, and the creasability which is claimed in this patent is a result of transesterification reactions of the polycarboxylic acids. This patent does not disclose or even speculate on any use or catalysis of methylol crosslinking reagents in conjunction with the polycarboxylic acids.